The present invention relates to a hydrocyclone adapted for the purification of liquid suspensions.
In the paper and pulp industry such a hydrocyclone has a wide range of uses for removing coarse and fine impurities and dirt particles from fiber-pulp water suspensions. Hydrocyclones are advantageous to use because they have no mechanically moving parts, they are relatively simple, their purification efficiency is high, and they have a long life.
A modern hydrocyclone comprises a relatively long conical tank, the widest part, i.e., base, of which is located at the top. In this part is located the liquid suspension inlet, which is tangential to the mantle surface of the cone. The suspension to be treated is introduced into the cyclone at a high velocity and is forced to revolve rapidly, whereby a vertical liquid vortex the shape of an inverted cone is produced which simultaneously gravitates continuously downwards. Dirt and, in general, parts heavier than water are pushed outwards by the centrifugal force towards the layer at the periphery and concentrate there. Owing to the conical shape of the cyclone the revolving liquid layer moves rapidly towards the apex of the cone and the bulk of the impurities separated from the suspension, i.e., the reject fraction, withdraws through the outlet at the apex of the cone. The purified liquid accumulates in the less mobile core of the revolving pillar, and an upward flow is produced in it towards the second outlet, which is a coaxial pipe which has been introduced through the upper end of the cyclone and extends over some distance into the base of the cyclone. The accept fraction is removed through this pipe.
In the paper and pulp industry, very great fiber suspension quantities are often involved which pass through the system within a time unit. Since hydrocyclones cannot be constructed very large, as their purification efficiency would thereby lower, suitably dimensioned cyclones are used side by side in batteries.
The use of batteries has proven effective and reliable. They have, however, certain drawbacks. Each individual cyclone is of a somewhat unsuitable shape in terms of coupling because it has two concentric outlets and a tangential inlet, which in practice are usually coupled with tubes and tube couplings. This results, however, in great losses of pressure. In addition, the cyclone system becomes relatively space-consuming.
From Swedish Pat. No. 315,266 is previously known a construction intended to eliminate the above drawbacks. It is characterized in that at the base of the hydrocyclone, between the cyclone mantle and the outlet pipe for the accept fraction, there are obliquely positioned plates, and the feed flow is introduced into the hydrocyclone tangentially through the clearance between the plates. Thus a tangential component is produced in the flow fed into the cyclone, and it aids the revolving of the liquid pillar inside the hydrocyclone. According to the said patent, openings in the walls of the hydrocyclone base can also be used for the tangential feeding (FIGS. 4, 4a and 5, 5a). In the latter case the flows which are fed impinge against each other since they are not directed at different vertical levels. This, again, results in excess turbulences causing a lowered hydrocyclone capacity. In the former case the feed flows arrive at different vertical levels so that the impinging of the feed flows against each other is avoided. In terms of flow technology, however, the presented method is not the best possible since the clearances between the plates cannot guide the sprays but the sprays are discharged in an indefinite direction.
Finnish Pat. No. 42,912 introduces a hydrocyclone with a screw-like end plate at the base. This has, however, only one feed inlet, which means increased instablity in the flow. Furthermore, one inlet requires a long guiding channel in comparison with a multi-inlet solution. This tends to increase the size of the apparatus. When one feed inlet is used the sprays do not impinge against each other so that in such a case the screw surface is only a guiding surface.
The object of the present invention is to provide a hydrocyclone with stable operation, in which the sprays discharging inside the classification pipe are prevented from impinging against each other